This invention relates to an improvement of joint for connecting together reinforcing bars which is called clip joint and disclosed in U.S. Pat. No. 4,695,178.
A joint includes sleeve 1 which is a hollow metallic pipe and has an opening respectively at the two ends and wedge 6, as shown in FIG. 5 and FIG. 6. The sleeve is formed in such as manner that the outer and inner peripheries thereof both have nearly an oval cross section, and the wall thereof includes of a pair of side walls 2 and 2' which are plane walls provided substantially parallel with each other at a certain spacing and a pair of curved walls 3 and 3' which are convex with respective to the center of the sleeve and connect the said side walls respectively. Wedge bores 4 and 4' are provided in the respective centers of said side walls in such a manner as to be aligned each other.
In operation, the connecting end portions of the reinforcing bars 5 and 5' respectively inserted into the upper and lower curved portions of sleeve 1 from the opposite sides thereof, and the wedge 6 is press-fitted into the area between the reinforcing bars 5 and 5' from one of the the wedge bores (4' in the FIGS. 5 and 6) to the other (4 in the FIGS. 5 and 6). Pressure applied at this time is usually about 10 tons. In consequence, the reinforcing bar 5 is pressed against the lower inner surface of the curved wall while the reinforcing bar 5' is pressed against the other inner surface so that the reinforcing bars 5 and 5' are connected strongly by the joint. This completes the connection of the reinforcing bars. The sleeve is usually about 5 to 10 cm long.
When the wedge 6 is press-fitted, strong pressure is applied to the respective arc centers 7 and 7' of the curved wall of the sleeve by the reinforcing bars which respectively contact the acr centers 7 and 7'. The pressure is greatest at the portion corresponding to the wedge insertion position of the arc center (i.e. at the center of the arc center in the longitudinal direction). Because of it, the arc centers of the respective curved walls should be reinforced. A reinforcing means employed is to make the portion to be reinforced thicker than the other portions. However, for convenience in manufacturing of sleeves, the whole sleeve is made as thick as the said reinforced portion in many cases, resulting in increase in cost of joint for connecting reinforcing bars.
Application of tensile force to the reinforcing bars connected together by the clip joint produces rotational force with the wedge as the fulcrum so that the sleeve slants slightly with respect to the direction of the tensile force as shown in FIG. 4. As a result, each of the edges of the arc centers of the curved walls which is at the opening of the said sleeve contacts strongly with the reinforcing bar which is press-fitted to the respective curved wall. In consequence, as the reinforcing bars come out little by little from the sleeve by the tensile force, the inserted bars are scraped off by the said edges so that the sectional area of the reinforcing bars decreases. The reinforcing bars connected by clip joint suffers from such a problem as to have smaller tensile strength than that of reinforcing bars with no such loss of sectional area. In addition, strong stress is produced at the opening of the sleeve by the said contact, and therefore the said portion must be reinforced to result in cost increase.